Assessing long-term actual daylighting performance of classrooms in-use
In the international effort to reduce carbon emissions, attention has been brought to obtaining energy from renewable sources. Daylight is such a natural and non-depleting energy source, with the potential to reduce electricity consumption and costs for lighting indoors and to contribute to the health and wellbeing of building occupants. For school buildings in particular, the Building Bulletin 90 of 1999 specifies that daylight is to be considered by designers as ‘the prime means of lighting when it is available’.
In 2013, the UK Education Funding Agency (EFA), responsible, by means of the Priority School Building Programme (PSBP), for a budget of over £4.4 billion toward new and refurbished schools, changed the daylight metrics used to specify mandatory daylight compliance of designs for government-funded schools. The new location and climate sensitive Climate Based Daylight Modelling (CBDM) metrics replaced the traditionally used Daylight Factor (DF), requiring designers to use daylight simulation tools. Evaluating whether this move will lead to improved daylighting performance of future classrooms requires the evidence-based understanding of how classrooms actually perform when in use.
Previous research has identified the importance of such knowledge for benchmarking daylight metrics and developing more realistic daylight models. However, it has also highlighted the limited amount of existing data from actual spaces (Konis, 2012; Mardaljevic et al, 2009), particularly from education buildings (Drosou 2015). This gap has led to even fewer studies that tackle the association of in-situ daylight level measurements with the occupants’ subjective assessments of daylight (Nong 2003, Parpairi 2002) and the actions they take to take to sustain or improve the luminous environment based on their visual needs.
AIMS AND OBJECTIVES
The project at hand addresses this gap, aiming to explore the extent to which UK government directives result in classrooms that satisfy the daylighting needs of the occupants.
The research objectives are the following:
- develop a robust methodology for monitoring long-term daylighting performance in classrooms;
- characterise the actual daylighting performance of a variety of classrooms based on luminance (a physical parameter of light);
- associate the recorded performance with observed actions the classrooms’ occupants take in order to satisfy their visual needs (electric light, blinds and Visual Display Technology [VDT] use);
- understand the rationale behind the observed behaviour by associating the occupants’ subjective evaluations of the luminous environment with the corresponding monitored values;
- establish whether the assessment of daylighting performance based on daylight standards is compatible with that based on the occupants’ subjective evaluations.
Four Leicestershire secondary school classrooms were used as case studies and a mixed method approach was applied.
High Dynamic Range imaging was used for monitoring luminance values, as well as electric light, blinds and VDTs status every 10 minutes daily over a period of one year.
Qualitative data was collected employing a Grounded Theory approach and performing a series of walkthroughs, interviews, questionnaires and focus groups.
The main dataset comprises over 60.000 images that are analysed both manually and with image processing software (IDL).
It is anticipated that the evidence-based and user-centred output of this project will affect different stakeholders in the following ways:
- policymakers: enhance their current understanding of the potential held by daylight specifications and metrics to result in classrooms that are well daylit in practice;
- design professionals: make modelling assumptions that are informed by both in-use classrooms in the real world and associated human factor issues, subsequently resulting to more realistic daylight (and effectively whole building energy) simulation outputs;
- academia: encourage the long-term study of real world occupied and complex environments of any type, in order to obtain the evidence necessary for benchmarking daylight metrics;
- students: perform classroom tasks in visually comfortable environments that are conducive to their health and wellbeing.
Images by Eleonora Brembilla (modelled classroom) and the author.